The commonly used mineral zinc, used to line the tins because of its anti-microbial qualities, leaches into the food and can alter the body's ability to absorb nutrients
TINNED tuna contains up to 100 times more zinc than is safe to eat, experts have warned.
They said the mineral could leach into the food, wrecking people's guts.
It's commonly used to line the inside of cans because of its anti-microbial qualities.
But it also seeps into food lodging in people's digestive system, altering the body's ability to absorb nutrients.
And in the long run it could potentially endanger health, warn scientists.
In the first study of its kind the US team at Binghamton University in New York looked at cans of sweetcorn, tuna, asparagus and chicken - and found some had 100 times the recommended dietary allowance.
Tinned chicken was the second most contaminated, followed by asparagus which had roughly two thirds of the levels found in tuna, while sweetcorn had around a third of the levels.
Zinc is second only to iron as the most abundantly found mineral in humans and is good for the skin, hair, teeth, nails, immune system - and even our libidos.
Prof Gretchen Mahler said: "It was found the zinc present in a serving of these foods is approximately one hundred times higher than the recommended dietary allowance."
Her team found tiny particles of zinc can settle in the digestive tract and alter it.
"We found zinc oxide nanoparticles at doses that are relevant to what you might normally eat in a meal or a day can change the way your intestine absorbs nutrients or your intestinal cell gene and protein expression."
Prof Mahler warned the mineral can also cause inflammation which makes the digestive tract more permeable or penetrable.
That's not a good thing, she warned.
"An increase in intestinal permeability is not a good thing," Prof Mahler said. "It means that compounds that are not supposed to pass through into the bloodstream might be able to."
The NHS said most of the recommended daily zinc dosage can be got from a normal diet, with rich sources including meat, shellfish, dairy such as cheese, bread and cereals.
A man aged 19 to 64 needs 9.5mg a day and women 7mg.
But zinc present in food packaging would put consumers at risk of ingestion of the nano particles.
There is little information on the amount of zinc in tins of food and the effects on the intestines from exposure.
The researchers have now taken the next step by using chickens to learn how an animal model responds to nanoparticle ingestion.
The findings are published in Food & Function.
